This invention relates to a vehiclar air-pollution preventive system. More particularly, it relates to a system for controlling the recirculation of exhaust gases back into the engine to the intake manifold only during certain vehicle operating conditions. No exhaust gas recirculation occurs when the specified conditions are not met.
The recirculation of exhaust gases into an internal combustion engine reduces the amount of unburned hydrocarbons and other undesirable elements that might otherwise pass into the atmosphere, and also reduces the oxygen availability to thereby lower the peak combustion temperatures and pressure and, therefore, oxides of nitrogen.
However, such recirculation hinders engine performance particularly during certain modes of engine operation. Continuous recirculation of the exhaust gases without reference to the engine operating parameters, as is generally the practice, results in unstable engine operation, decreased engine output, and contamination within the engine and, as such, is considered unsuitable for practical purposes. The present invention, provides for selectively recirculating exhaust gases only when the vehicle is driven under predetermined conditions in which the quantity of nitrogen oxides normally emitted would be of consequence.
Other exhaust gas recirculation systems for selectively recirculating exhaust gases have been devised. For example, U.S. Pat. Nos. 3,646,764 and 3,636,934, both to Nakajima, et al., disclose a normally closed solenoid valve which governs recirculation to the intake manifold which is activated by a signal passing through a plurality of series connected switches. Each switch is dependent upon an engine operating parameter and is closed allowing the signal to pass only when that parameter is above a preselected valve. However these devices have not been practical because of the additional expense and space required by the parameter responsive switches and their wiring and most significantly because the solenoid valve has to be very large to allow the required exhaust gas recirculation flow into the intake manifold. This requires a very expensive solenoid valve and puts a large drain on the battery for activation. In addition, the use of the parameter control switches is not very accurate or quickly responsive.
U.S. Pat. No. 3,768,452 to Lewis uses two vacuum control valves connected serially to allow exhaust gas recirculation except at idle and wide open throttle. However, accuracy is severely limited as recirculation depends only upon one parameter-intake manifold vacuum, and is limited to the accuracy and activation time of a spring which is subject to large hysteresis effects. Similarly, U.S. Pat. No. 3,783,847 to Kolody discloses a vacuum operated valve which controls exhaust gas recirculation. The vacuum applied is either spark port vacuum or e.g.r. port vacuum which is dependent upon the position of a solenoid actuated selector valve. The solenoid valve is actuated by a circuit employing engine parameter sensitive switches which are closed when the respective engine parameters are above pre-selected values. In this patent, the vacuum rather than being selectively applied to the vacuum responsive control valve, is constantly applied. Also, this invention is subject to the problems of accuracy, space, and expense in employing the parameter sensitive switches and the severe accuracy and response time problems should the spring in the vacuum control valve be used as a selective control for injection of exhaust gases.